There has been much interest raised by the recent discovery that different autosomal dominant point mutations within the gene encoding for LRRK2 predispose humans to develop late-onset PD (OMIM accession number 609007), with a clinical appearance indistinguishable from idiopathic PD [1-3]. The genetic analysis undertaken to date indicates that mutations in LRRK2 are relatively frequent, not only accounting for 5-10% of familial PD, but also being found in a significant proportion of sporadic PD cases [4, 5]. Little is known about how LRRK2 is regulated in cells, what its physiological substrates are and how mutations cause or increase risk of PD.
The domain structure of LRRK2 is shown in FIG. 1, which also depicts the mutations that have thus far been reported in patients with PD. The defining feature of the LRRK2 enzyme is a Leucine Rich Repeat (LRR) motif (residues 1010-1291), a Ras-like small GTPase (residues 1336-1510), a region of high amino acid conservation that has been termed the C-terminal of Ras of complex (COR) domain (residues 1511-1878), a protein kinase catalytic domain (residues 1879-2132) and a C-terminal WD40 motif (2231-2276) [6, 7]. The protein kinase domain of LRRK2 belongs to the tyrosine-like serine/threonine protein kinases and is most similar to the kinase RIP (Receptor Interacting Protein), which play key roles in innate immunity signalling pathways [8]. To date, almost 40 single amino acid substitution mutations have been linked to autosomal-dominant PD and the location of these mutations is illustrated in FIG. 1 ([2, 3]). The most prevalent mutant form of LRRK2 accounting for approximately 6% of familial PD and 3% of sporadic PD cases in Europe, comprises an amino acid substitution of Gly2019 to a Ser residue. Gly2019 is located within the conserved DYG-Mg2+-binding motif, in subdomain-VII of the kinase domain [2]. Recent reports suggest that this mutation enhances the autophosphorylation of LRRK2, as well as its ability to phosphorylate myelin basic protein 2-3-fold [9, 10], a finding confirmed by the Applicant [11]. These observations suggest that over-activation of LRRK2 predisposes humans to develop PD, implying that drugs which inhibited LRRK2, could be utilised to halt progression or even perhaps reverse symptoms of some forms of PD.
The study of LRRK2 has been hampered by the difficulty in expressing active recombinant enzyme and by the lack of a robust quantitative assay. In work undertaken by the Applicant, an active recombinant fragment of LRRK2 containing the GTPase-COR and kinase domains encompassing residues 1326-2527 was expressed in 293 cells [11]. The more active G2019S mutant of this LRRK2 fragment was utilised in a KinasE Substrate TRacking and ELucidation (KESTREL) screen in an initial attempt to identify physiological substrates (reviewed in [14]). This led to the identification of a protein termed moesin, which was efficiently phosphorylated by LRRK2 in vitro [11]. Moesin is a member of the Ezrin/Radixin/Moesin (ERM) family of proteins which functions to anchor the actin cytoskeleton to the plasma membrane and plays an important role in regulating membrane structure and organization [15, 16]. It was found that LRRK2 phosphorylated moesin at Thr558 [11], a previously characterised physiologically relevant phosphorylation site [15, 16]. LRRK2 also phosphorylated ezrin and radixin at the equivalent Thr residue. Phosphorylation of ERM proteins at the residue equivalent to Thr558, opens up the structures of these proteins and enables them to interact with actin microfilaments at their C-terminal residues and phosphoinositides and plasma membrane proteins through an N-terminal FERM domain. These findings were utilised to develop a robust and quantitative assay for LRRK2, based upon the phosphorylation of moesin or a short peptide that encompasses the Thr558 residue of moesin which is also efficiently phosphorylated by LRRK2 [11]. These assays were further adapted to develop an improved assay based on the use of the Nictide peptide [17].
The present invention seeks to provide compounds that are capable of inhibiting one or more kinases, more particularly, LRRK, even more preferably LRRK2.